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i.nightlights.intercalibration is a GRASS GIS module performing
inter-satellite calibration on DMSP-OLS nighttime lights time series.
Based on "well known" emprirical regression models, it
calibrates average visible band Digital Number values.

"Several methods were proposed to overcome the lack of inter-satellite
calibration. These include the invariant region and the quadratic regression
method proposed by Elvidge et al. [23], the second-order regression and optimal
threshold method proposed by Liu et al. [24], and a power-law regression method
proposed by Wu et al. [25]. Although studies based on these calibration methods
showed performance improvement after the rectification [24,25], the assumption
that the nighttime light remains stable over time in a particular area requires
a careful choice of the invariant region manually." [Huang 2014]